[Suicide Junkie]

-Player has already built the ship that he is going to construct BEFORE, so the maintenance cost is known. [sorry guys, thats the only way i know how to get the maintenance values. if someone has a better way, please let me know!]

Start at 25%. Subtract your maintenance reduction racial characteristic. (Commonly boosted to 20%; 25%-20% = 5%)
This is your actual maintenance cost per turn.

Multiply you ship's build cost by the above maintenance rate.
If you are looking at a base, rather than a ship, divide by 2.

If you have a crystalline restructuring plant in the system, take off another 5 to 15% depending on tech level.

This is how much you spend each turn for maintenance.